5. Green Clay of St. Peter's.—This differs little from the preceding, except in its color, which is a deep or verdigris green, admitting some diversity of shades. Its composition appears to be, essentially, alumina, silica, carbonate of copper, water, and iron.
6. Opwagunite; Calamet Stone; Pipe Stone.—The last of these terms is a translation of the first, which is Algonquin. Under these names, a peculiar kind of stone, which is much employed by the Indians for pipes, has been alluded to by travellers and geographers from the earliest times. It appears to be a variety of argillaceous wacke. Its color is most commonly a uniform dull red, resembling that of red chalk. Sometimes it is spotted with brown or yellow, but these spots are very minute, and the colors usually faint. It is perfectly opaque, very compact in its structure, and possessing that degree of hardness which admits its being cut or scraped with a knife, or sawed without injury to a common hand-saw, when first raised from the quarry; but it acquires hardness by exposure, and even takes a polish. But it is not capable of receiving a polish by the usual process of rubbing with grit-stone and pumice, these substances being too harsh for it. The Indian process is to scrape or file it smooth, and give it a polish by rubbing with the scouring rush. Its powder is a light red, and emits an argillaceous odor when wetted. This substance is procured at the Coteau des Prairie, intermediate between the sources of the St. Peter's and the Great Sioux Rivers. Some other places have been mentioned as affording this mineral, particularly a locality on the waters of Chippewa River; but the mineral procured here is chocolate-colored.
e. Magnesian Minerals.
1. Serpentine.
At Presque Isle Point, Lake Superior, common and precious, in isolated masses; also, in connection with, and imbedding native copper, along the southern shore of Lake Superior, at Ontonagon River, &c.
2. Steatite.
At Presque Isle, near River au Mort, Lake Superior, in connection with the serpentine formation. Also, at the Lake of the Woods, of a black or very dark color, where it is employed by the Indians in carving pipes.
3. Asbestos.
Common Asbestos.—In serpentine and steatite, at Presque Isle Point, Lake Superior. Also, in minute veins, in detached masses of diallage and serpentine rocks, on the west shore of Lake Michigan. These veins are no more than a fourth of an inch in width; and the fibres of asbestos occur transversely. They are very flexible, and easily reducible into a flocculent mass.
f. Barytic Minerals.
Sulphate of Barytes.
Lamellar Sulphate of Barytes.—In detached masses, imbedded in diluvial soil, at the mines of Peosta, or Dubuque, on the Upper Mississippi, where it is accompanied by sulphuret of lead, calcareous spar, &c. Also, at the Mine au Fevre (now Galena), and at the mouth of the Sissinaway River, on the east banks of the Mississippi, between Prairie du Chien and Fort Armstrong. Its colors are white or yellow, and it is frequently incrusted with a thin coat of yellow oxide of iron. It is most commonly opaque. The only translucent specimen seen was procured at Dubuque's mines.